The present invention relates to a vehicle current drain tester and, more particularly, to a tester having a vehicle memory saver.
A typical vehicle electrical system includes a battery which powers an ignition system and various accessories, such as lights, a radio, power windows, a clock, an on-board computer and associated memory. Present day vehicles have a small amount of current drain on the vehicle battery even when the engine is not running. When the engine is not running, the battery must still provide power to certain accessories, such as the clock and the on-board computer memory. In a properly operating vehicle, the nominal current drain on the battery preferably does not drain the battery to less than 50% of the state of charge in four to five weeks if the vehicle is not driven during that period. The actual time for discharge could vary depending upon the size of the battery and the actual vehicle current drain.
Nominal current drain can be measured by disconnecting the vehicle's ground cable from the negative battery terminal and measuring the current between these two points with an ampere-meter. The resulting current reading is an indication of the nominal current drain on the battery. However, the ampere-meter introduces an additional load into the circuit which changes the current and causes the current reading to be different from the nominal current drain on the battery. The operator must correct the current reading to cancel the effects of connecting the amperemeter into the circuit and then compare the corrected current reading with a specification for the vehicle being tested. This procedure requires a relatively skilled operator and even then is susceptible to errors in the current reading itself or in the correction. The procedure also consumes a relatively large amount of time since corrections must be made and then analyzed before a pass/fail determination can be made.
Another problem associated with traditional ampere-meters is that the operator must first select an appropriate ampere range for the measurement, such as a milliamp range. If the selected range is too small, connecting the meter into the circuit will "blow" a safety fuse in the meter. The fuse must then be replaced. Even if the correct range is selected for a vehicle's nominal current drain, the operator may mistakenly open a vehicle door or turn on an accessory which greatly increases the current flow through the meter resulting in another blown fuse. Traditional ampere-meters also have small clip leads which are not well suited for automotive applications. The small clip leads are difficult to clip to large automotive parts and typically have too short connecting leads.
Also, when disconnecting the battery to make the current drain measurement or to replace or recharge the battery, it is desirable to supply current to the vehicle memory and the clock to prevent losing data or disrupting the clock. Several different devices have been used to provide stand by power to the vehicle, such as battery packs or power packs, which plug into a 110 Volt AC line. Power is supplied to the vehicle through the cigarette lighter or through the vehicle battery cables before the battery is disconnected. These devices are typically expensive and inconvenient to use.